One-dimensional markers and two-dimensional markers (e.g., QR code (registered trademark)) are widely used in information processing systems as rapid and inexpensive means for reading information. Along with the popularization of mobile terminals, various techniques have been developed for reading information stored in the markers.
For example, a technique is known that recognizes a marker included in an image by combining straight lines obtained by edge detection. When the recognition fails, the recognition processing repeats until the marker is successfully recognized by reusing the combination results of the multiple straight lines. Another technique is used that recognizes a marker on the basis of a ruled-based system using color information about an image. In the technique, ID stored in the marker is recognized as follows: a binarized input image is further subjected to blurring processing, an area that includes more than a certain rate of black pixels and satisfies the feature of the marker is set as a marker area, and information on enumeration of white segments or black segments is estimated from white-and-black information in the area to regenerate the marker and recognize the ID.
It is difficult for the conventional technique, however, to detect the edges when the marker is small or the marker is imaged at a far distance from the marker because position detection patterns included in the marker of an image become small. Furthermore, noises increase due to an imaged background and thus the position detection patterns fail to be detected. As a result, the location of the marker fails to be found in the image.